Grid



Sept. 16, 1941. s UMBRE|T 2,255,906

GRID

Filed June 27, 1940 DIFFERENT WIRES 0F I *zf DIFFERENT g [mums/now 'w a a 2 HVVENTOR STANTON UMBREIT ATTORNEY Patented Sept. 16, 1941 GRID Stanton Umbreit, West Orange, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 27, 1940, Serial No. 342,599

Claims.

My invention relates to grid electrodes for electron discharge devices.

For some types of radio tubes it is advantageous to use grids which have different kinds of grid Wires or conductors at different points along the length of the grid. For example, it has been proposed to make a helically wound grid in which the grid wire is of greater diameter at one end of the grid helix than at the other. Such a grid can be made only with a tapered grid wire, which is not practical. In operation diiferent portions of a radio tube grid are subjected to different temperature and other operating conditions. The space current in many tubes is limited by the maximum temperature at which the grid may be operated, and emission from the grid and variable contact potential usually result at the high temperature portions of the grid. Making different parts of the grid of wires of different metals is advantageous, but to make such a grid of the conventional helical type is not feasible.

The object of my invention is an improved grid which is inexpensive and commercially feasible to manufacture, and in which any portion of the grid may be made of grid conductors of a selected size and composition.

The characteristic features of my invention are defined in the appended claims and preferred embodiments are described in the following specification and shown in the accompanying drawing in which Figure 1 shows in perspective my novel grids in the processes of manufacture, Figure 2 shows an end view of the grids of Figure 1, Figure 3 shows in section an electron discharge device with an electrode assembly containing my improved grid, and Figure 4 is a detailed View in perspective of my improved grid.

My improved grid comprises two spaced parallel support or side rods l and a plurality of parallel grid conductors or wires 2 transverse to the side rods and each joined at its end to the side rods, preferably by welding. These grids may conveniently be made as indicated in Figure 1 and more fully described in the Kershaw Patents 2,004,246, June 11, 1935, and 2,064,169, December 15, 1936, by feeding the relatively heavy side rod material into a welding machine in a direction at right angles to the grid wires. Each grid wire is unreeled from a separate spool, not shown, and for proper spacing is threaded through the teeth of a comb 3. Two sets of wires and two combs are employed for a complete cylindrical grid with grid wires attached to opposite sides of the side rods. As the grid wires are pulled over the side rods, welding electrodes 4 draw the wires over the mandrels 5 and press the wires into contact with the side rods I, whereupon current is passed between the welding electrodes to weld the wire to the side rods. The completed grid is cut off by shears 6.

' Each grid is then mounted in the usual way in an electrode assembly, as shown in Figure 3, by passing the ends of the side rods through spacers l, which also hold the ends of cathode 8 and anode 9.

I have found that for a conventional radio tube, in which the cathode is hottest near the middle portion, a suitable grid for high temperature operation without objectionable grid emission and without sagging may be obtained. if the wires at the middle of the grid are made of a metal which has high hot strength, such as molybdenum or chromium-nickel alloy, and the end wires of less. expensive metal, such as nickel or a nickel alloy, such as manganese nickel.

Where the central wires IU of the grid are larger in diameter than the end wires, two welding steps for each grid are required. Welding electrodes 4 may be of such a length longitudinally of the side rods as to weld first one group of wires of one diameter and a second set of welding electrodes then following to weld the second group of wires. High temperature brazing or soldering may of course be substituted for weldmg.

My improved grid is easy and inexpensive to manufacture and, not being limited by wire size or composition, is easily adapted to all tube designs. My improved grid, although made only in part of expensive high temperature metal, may be used in tubes operated at high power and high temperature levels. In addition to grid .wires with different sizes and composition, the wires may conveniently be made with different shapes of cross section. Some of the wires, for example, may be flattened and attached to the side rods with narrow side of the wire facing in a radial direction. My improved grid, without increasing cost, may be operated at high temperatures in tubes with high trans-conductance and high amplification factors with minimum grid emission and contact potential variations.

I claim:

1. A grid comprising two spaced parallel side rods, a plurality of individual parallel grid Wires transverse to said rods, each grid wire being joined at opposite ends to said rods, one grid wire having greater heat conductivity than the next adjacent wire.

2. A grid electrode comprising a support rod,

NT one:

a plurality of side-by-side wires, each attached at one end to said rod, one of said wires having a composition different from the next adjacent wire. I

3. In combination, a cathode, an anode a grid,

'said grid comprising a support rod and a plurality of grid wires between the cathode and anode attached to said rod, different wires being of different metals. V

4. A grid comprising two parallel support rods,

a plurality of side-by-side grid wires, each wire being attached at opposite ends to said rods, and at least one of said wires being of different size than adjacent wires.

5. A grid electrode comprising a support rod, a group of side-by-side wires attached to one portion of said rod, said wires being made of a nickel alloy of high hot strength, another group of side-by-side wires attached to another portion of said rod, the secondgroup of wires being made 7 10 of a difierent nickel alloy.

STANTON UMBREIT. 

